For a semiconductor device such as a liquid crystal display device, a polysilicon film that is obtained by poly-crystallizing a non-crystalline silicon film such as an amorphous silicon film is widely used as a semiconductor film.
Further, in recent years, for a liquid crystal display device equipped with semiconductor elements such as thin film transistors (TFTs) and optical sensors such as photodiodes, the above-mentioned polysilicon film has been used as the semiconductor films for the TFTs and the optical sensors.
As a method for poly-crystallizing an amorphous silicon film, a method of poly-crystallizing an amorphous silicon film to change to a polysilicon film by irradiating the amorphous silicon film with laser light has been suggested. A pulse laser such as an excimer laser is commonly used as the laser, and by irradiating an amorphous silicon film with linear-shaped laser light for multiple times, a polysilicon film of an approximate crystal grain size of 0.5 μm can be formed. In recent years, technologies such as poly-crystallization by CW laser or quasi-CW laser, and the SLS method using pulse laser are also available, and it is possible to grow long and thin shaped crystal with the length of several tens of μm, which expands in the scanning direction of laser light (in other words, lateral growth).
Moreover, in a liquid crystal display device equipped with semiconductor elements such as TFTs and optical sensors, in order to prevent malfunction of the semiconductor device by preventing the increase in off-currents caused by the irradiated light from a backlight entering to a channel region of a polysilicon film that constitutes the semiconductor element, a light-shielding film for controlling the light entering to the channel region of the polysilicon film is commonly formed.
More specifically, as shown in FIG. 41(b), a liquid crystal display device that includes a transparent insulating substrate 61 such as a glass substrate, a light-shielding film 62 made of a metal such as Mo formed over the insulating substrate 61, an insulating film 63 made of silicon oxide film or the like formed over the light-shielding film 62, and a polysilicon film 64 formed by irradiating an amorphous silicon film 69 formed over the insulating film 63 with laser light L to poly-crystallize the amorphous silicon film 69 is disclosed (for example, refer to Patent Document 1).